In recent years, for example in corporations that handle big data, demand has increased for use, in storage systems, of solid state drives (SSDs) that are high speed and low in power consumption.
As in the example illustrated in FIG. 32, a conventional storage system is configured as a multilevel hierarchy with servers, disk arrays, SSDs, NAND flash memories, and the like. At each level of the hierarchy, data is provided with redundancy and error correction is performed, thereby improving reliability.
A variety of types of Redundant Arrays of Independent Disks (RAID) have also been proposed as techniques for combining a plurality of memory devices to improve reliability (for example, see Mike Ault, “Oracle and RAID Usage” (NPL 1)).